Ecological Causes of High Morphological Plasticity of Members of a Taxon Inhabiting the Center of Its Origin (Exemplified by the Noble Salmons, Genus Salmo)

Abstract

As molecular genetic data have shown, the center of origin of the genus Salmo is located in the Ponto-Caspian basin; according to the criteria proposed by N.I. Vavilov, it is in the modern Caucasus region. In this region, the noble salmons occupy various ecological niches and display a high morphological and ecological diversity, which is supported to a significant extent by their phenotypic plasticity. In other parts of the range, the phenotypic plasticity of Salmo decreases as a result of genetic assimilation and immobilization. This can probably be explained by the fact that the center of origin coincides with the ecological optimum of the group, which is, consequently, exposed to a minimum selection pressure in the region. Outside the center, the directional and stabilizing selections are stronger and reduce the morphological and ecological diversity of the group.